U.S. patent application number 12/296748 was filed with the patent office on 2010-01-28 for solar cell, solar cell string and solar cell module.
Invention is credited to Masaomi Hioki, Toshio Kimura, Takahisa Kurahashi, Akira Miyazawa, Kyotaro Nakamura, Hirotaka Sato.
Application Number | 20100018562 12/296748 |
Document ID | / |
Family ID | 38609161 |
Filed Date | 2010-01-28 |
United States Patent
Application |
20100018562 |
Kind Code |
A1 |
Kurahashi; Takahisa ; et
al. |
January 28, 2010 |
SOLAR CELL, SOLAR CELL STRING AND SOLAR CELL MODULE
Abstract
A solar cell includes a semiconductor substrate having a
photoelectric converting portion, a first electrode formed on a
first main surface of the semiconductor substrate, and a second
electrode connected to the first electrode on the first main
surface. The first electrode includes a plurality of first
connecting portions to be connected to an interconnector and a
first non-connecting portion not connected to an interconnector.
The first non-connecting portion is arranged between first
connecting portions to electrically connect the first connecting
portions together. The first connecting portion and first
non-connecting portion are coupled forming an angle larger than
90.degree. and smaller than 180.degree.. A solar cell string and a
solar cell module employ the solar cells.
Inventors: |
Kurahashi; Takahisa; (Nara,
JP) ; Sato; Hirotaka; (Nara, JP) ; Miyazawa;
Akira; (Nara, JP) ; Nakamura; Kyotaro; (Nara,
JP) ; Kimura; Toshio; (Nara, JP) ; Hioki;
Masaomi; (Nara, JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Family ID: |
38609161 |
Appl. No.: |
12/296748 |
Filed: |
March 15, 2007 |
PCT Filed: |
March 15, 2007 |
PCT NO: |
PCT/JP2007/055171 |
371 Date: |
September 9, 2009 |
Current U.S.
Class: |
136/244 ;
136/256 |
Current CPC
Class: |
Y02E 10/50 20130101;
H01L 31/022433 20130101; H01L 31/0508 20130101 |
Class at
Publication: |
136/244 ;
136/256 |
International
Class: |
H01L 31/042 20060101
H01L031/042; H01L 31/00 20060101 H01L031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 2006 |
JP |
2006-112232 |
Jul 13, 2006 |
JP |
2006-192542 |
Claims
1. A solar cell comprising: a semiconductor substrate having a
photoelectric converting portion, a first electrode formed on a
first main surface of said semiconductor substrate, and a second
electrode connected to said first electrode on said first main
surface, wherein said first electrode includes a plurality of first
connecting portions to be connected to an interconnector, and a
first non-connecting portion not connected to an interconnector,
said first non-connecting portion is arranged between said first
connecting portions, electrically connecting said first connecting
portions together, and said first connecting portion and said first
non-connecting portion are coupled forming an angle larger than
90.degree. and smaller than 180.degree..
2. The solar cell according to claim 1, wherein said first
non-connecting portion extends from an end face of said first
connecting portion.
3. The solar cell according to claim 1, wherein said first
non-connecting portion extends from a side face of said first
connecting portion.
4. The solar cell according to claim 1, wherein said first
non-connecting portion is formed of a combination of straight
portions.
5. The solar cell according to claim 1, wherein said first
non-connecting portion includes an arc portion.
6. The solar cell according to claim 1, wherein a cross-sectional
area of said first non-connecting portion is not more than 1/2 the
cross-sectional area of said first connecting portion.
7. The solar cell according to claim 1, wherein at least one of
said first connecting portions adjacent to an end of said first
main surface is arranged apart from the end of said first main
surface.
8. The solar cell according to claim 1, wherein a second connecting
portion to be connected to an interconnector and a second
non-connecting portion not connected to an interconnector are
formed alternately on a second main surface opposite to said first
main surface of said semiconductor substrate.
9. The solar cell according to claim 8, including a portion where
said first connecting portion and said second connecting portion
are located symmetric about said semiconductor substrate.
10. A solar cell string comprising a plurality of solar cells
defined in claim 8 connected, said solar cells adjacent to each
other, wherein said first connecting portion of a first solar cell
and said second connecting portion of a second solar cell are
electrically connected by an interconnector.
11. The solar cell string according to claim 10, wherein said
interconnector is bent between said first solar cell and said
second solar cell.
12. The solar cell string according to claim 10, wherein a small
cross-sectional area section having a cross-sectional area of said
interconnector locally reduced is arranged at at least one of a
site corresponding to an inside region, adjacent to a side face of
said first non-connecting portion and an end face of said first
connecting portion and a site corresponding to said second
non-connecting portion.
13. A solar cell module comprising the solar cell string defined in
claim 10 sealed with a sealant.
14. The solar cell according to claim 1, wherein a surface contour
of an inside region adjacent to a side face of said first
non-connecting portion and an end face of said first connecting
portion takes an arc shape at leading ends located at a side of a
first connecting portion.
15. The solar cell according to claim 14, wherein the surface
contour of said inside region takes a circular, an ellipse, or a
track shape.
16. The solar cell according to claim 14, wherein a second
connecting portion to be connected to an interconnector and a
second non-connecting portion not connected to an interconnector
are formed alternately on a second main surface opposite to said
first main surface of said semiconductor substrate.
17. The solar cell according to claim 16, wherein a length of said
inside region in a direction of arrangement of said first
connecting portion and said first non-connecting portion is shorter
than the length of said second non-connecting portion, facing said
inside region with said semiconductor substrate therebetween, in a
direction of arrangement of said second connecting portion and said
second non-connecting portion.
18. The solar cell according to claim 16, including a portion where
said second non-connecting portion is not formed at a location
symmetric to the location where said inside region is formed about
said semiconductor substrate.
19. A solar cell string comprising a plurality of solar cells
defined in claim 16 connected, said solar cells adjacent to each
other, wherein said first connecting portion of a first solar cell
and said second connecting portion of a second solar cell are
electrically connected by an interconnector.
20. The solar cell string according to claim 19, wherein a small
cross-sectional area section having a cross-sectional area of said
interconnector reduced locally is arranged at at least one of a
site corresponding to said inside region and a site corresponding
to said second non-connecting portion.
21. A solar cell module comprising the solar cell string defined in
claim 19 sealed with a sealant.
Description
TECHNICAL FIELD
[0001] The present invention relates to solar cells, solar cell
strings, and solar cell modules. Particularly, the present
invention relates to a solar cell, a solar cell string, and a solar
cell module that can have generation of a crack in a solar cell
reduced when warpage occurs in the solar cell during a cooling step
subsequent to connection of an interconnector.
BACKGROUND ART
[0002] Expectations for a solar cell that directly converts
sunlight energy into electric energy as the energy source for the
next generation has rapidly grown these few years particularly from
the standpoint of global environmental problems. Among the various
types of solar cells employing a compound semiconductor or an
organic material, a solar cell employing silicon crystal is now the
main stream.
[0003] FIG. 26 represents a schematic sectional view of an example
of a conventional solar cell. The solar cell has an n+ layer 11
formed at the light-receiving face of a p-type silicon substrate
10. A pn junction is formed by p-type silicon substrate 10 and n+
layer 11. An anti-reflection film 12 and a silver electrode 13 are
formed on the light-receiving face of p-type silicon substrate 10.
Further, a p+ layer 15 is formed at the back side of p-type silicon
substrate 10, opposite to the light-receiving face. In addition, an
aluminium electrode 14 and a silver electrode 16 are formed on the
back side of p-type silicon substrate 10. The aforementioned pn
junction corresponds to a photoelectric conversion portion at
p-type silicon substrate 10.
[0004] FIG. 27 (a)-(i) represents an example of a fabrication
method of a conventional solar cell. First, as shown in FIG. 27(a),
a silicon ingot 17 obtained by dissolving p-type silicon crystal
material in a crucible and recrystallizing the material is cut into
silicon blocks 18. As shown in FIG. 27(b), a silicon block 18 is
cut with a wire saw to produce a p-type silicon substrate 10.
[0005] Then, the surface of p-type silicon substrate 10 is etched
using alkali or acid to remove a damage layer 19 generated during
the slicing process of p-type silicon substrate 10 shown in FIG.
27(c). At this stage, microscopic asperities (not shown) can be
formed at the surface of p-type silicon substrate 10 by adjusting
the etching conditions. The asperities are advantageous in that
reflection of sunlight incident on the surface of p-type silicon
substrate 10 is reduced to allow the photovoltaic conversion
efficiency of the solar cell to be improved.
[0006] Subsequently, as shown in FIG. 27(d), a dopant solution 20
containing a compound including phosphorus is applied on one main
surface (hereinafter, referred to as "first main surface") of
p-type silicon substrate 10. By heating p-type silicon substrate 10
with dopant solution 20 applied for 5 to 30 minutes at the
temperature of 800.degree. C. to 950.degree. C. to cause diffusion
of phosphorus that is an n type dopant at the first main surface of
p-type silicon substrate 10, an n+ layer 11 is formed at the first
main surface of p-type silicon substrate 10, as shown in FIG.
27(e). The method of forming n+ layer 11 includes a method of vapor
phase diffusion using P.sub.2O.sub.5 or POCl.sub.3 in addition to
the method of applying a dopant solution.
[0007] Following the removal of a glass layer formed at the first
main surface of p-type silicon substrate 10 at the time of
phosphorus diffusion by an acid treatment, an anti-reflection film
12 is formed on the first main surface of p-type silicon substrate
10, as shown in FIG. 27(f). Known methods to form anti-reflection
film 12 includes a method of forming a titanium oxide film by means
of atmospheric pressure CVD, and forming a silicon nitride film by
means of plasma CVD. In the case where phosphorus is to be diffused
by the method of applying a dopant solution, the usage of a dopant
solution containing the material of anti-reflection film 12 in
addition to phosphorus allows simultaneous formation of n+ layer 11
and anti-reflection film 12. There are also cases where
anti-reflection film 12 is formed after formation of a silver
electrode.
[0008] As shown in FIG. 27(g), an aluminium electrode 14 is formed
on the other main surface (hereinafter, referred to as "second main
surface") of p-type silicon substrate 10. In addition, a p+ layer
15 is formed at the second main surface of p-type silicon substrate
10. The formation of aluminium electrode 14 and a p+ layer 15 can
be carried out as set forth below. For example, aluminium paste
composed of aluminium powder, glass frit, resin and an organic
solvent is applied by screen-printing and the like, followed by
heat-treating p-type silicon substrate 10 for fusion of aluminium
to generate an alloy with silicon, resulting in the formation of an
aluminium-silicon alloy layer. Under this aluminium-silicon alloy
layer, p+ layer 15 is formed. In addition, aluminium electrode 14
is formed on the second main surface of p-type silicon substrate
10. The difference in the dopant concentration between p-type
silicon substrate 10 and p+ layer 15 causes a potential difference
(acting as a potential barrier) at the interface between p-type
silicon substrate 10 and p+ layer 15, which prevents
optically-generated carriers from recoupling in the proximity of
the second main surface layer of p-type silicon substrate 10.
Accordingly, the short-circuit current (Isc) and the open circuit
voltage (Voc) of the solar cell are both improved.
[0009] Then, a silver electrode 16 is formed on the second main
surface of p-type silicon substrate 10, as shown in FIG. 27(h).
Silver electrode 16 can be produced by printing silver paste
composed of silver powder, glass frit, resin, and an organic
solvent by means of screen-printing and the like, followed by
heat-treating p-type silicon substrate 10.
[0010] Then, a silver electrode 13 is formed on the first main
surface of p-type silicon substrate 10, as shown in FIG. 27(i). The
pattern design such as the line width, pitch, thickness and the
like of silver electrode 13 is crucial for the purpose of setting
low the series resistance including the contact resistance with
p-type silicon substrate 10 and also reducing the area where silver
electrode 13 is formed to avoid reduction in the incident sunlight.
An exemplified method of forming silver electrode 13 includes the
steps of applying silver paste composed of silver powder, glass
frit, resin, and an organic solvent on the surface of an
anti-reflection film 12 by screen-printing, for example, and
heat-treating p-type silicon substrate 10 to cause passage of the
silver paste through anti-reflection film 12, allowing favorable
electrical contact with the first main surface of p-type silicon
substrate. This fire-through process is employed in a mass
production line.
[0011] A solar cell structured as shown in FIG. 26 can be
fabricated as set forth above. A solder coat may be applied on the
surface of silver electrodes 13 and 16 by immersing p-type silicon
substrate 10 having silver electrodes 13 and 16 formed in a molten
solder bath. This solder coating step may be omitted depending upon
the process. Furthermore, the solar cell fabricated as set forth
above may be irradiated with pseudo sunlight using a solar
simulator to measure the current-voltage (IV) characteristics of
the solar cell to test the IV characteristics.
[0012] A plurality of solar cells are connected in series to
constitute a solar cell string. Then, the solar cell string is
sealed with a sealant to be offered for sale and usage in the form
of a solar cell module.
[0013] FIG. 28(a)-(e) represents an example of a fabrication method
of a conventional solar cell module. Referring to FIG. 28(a), an
interconnector 31 that is a conductive member is connected on the
silver electrode at the first main surface of solar cell 30.
[0014] Referring to FIG. 28(b), a row of solar cells 30 having
interconnector 31 connected are arranged. Interconnector 31
connected to the silver electrode located at the first main surface
of a solar cell 30 has its other end connected to the silver
electrode located at the second main surface of another solar cell
30. Thus, a solar cell string 34 is produced.
[0015] Referring to FIG. 28(c), the solar cell strings are arranged
and connected with each other by connecting in series an
interconnector 31 protruding from both ends of a solar cell string
with an interconnector 31 protruding from both ends of another
solar cell string by means of a wiring material 33 that is a
conductive member.
[0016] Referring to FIG. 28(d), the connected solar cell string 34
is sandwiched between EVA (ethylene vinyl acetate) films 36,
identified as a sealing member, and then further sandwiched between
a glass sheet 35 and a back film 37. The air bubbles present
between EVA films 36 are removed by reducing the pressure, and heat
treatment is applied. Accordingly, EVA film 36 is cured, whereby
the solar cell string is sealed in the EVA. Thus, a solar cell
module is produced.
[0017] Referring to FIG. 28(e), the solar cell module is placed in
an aluminium frame 40. A terminal box 38 including a cable 39 is
attached to the solar cell module. Then, the solar cell module
produced as set forth above is irradiated with pseudo sunlight
using a solar simulator to measure the current-voltage (IV)
characteristics of the solar cell to test the IV
characteristics.
[0018] The schematic plan view of FIG. 29 represents the
configuration of silver electrode 13 formed on the first main
surface of p-type silicon substrate 10, which will be the
light-receiving face of the solar cell of FIG. 26. Silver electrode
13 is formed including one linear bus bar electrode 13a of a
relatively large width, and a plurality of linear finger electrodes
13b of a relatively small width, extending from bus bar electrode
13a.
[0019] The schematic plan view of FIG. 30 represents the
configuration of aluminium electrode 14 and silver electrode 16
formed on the second main surface of p-type silicon substrate 10,
identified as the back side of the solar cell of FIG. 26. Aluminium
electrode 14 is formed nearly all over the second main surface of
p-type silicon substrate 10, whereas silver electrode 16 is formed
only at a portion of the second main surface of p-type silicon
substrate 10. Silver electrode 16 that allows a solder coat to be
applied may be required since it is difficult to apply a solder
coat on aluminium electrode 14.
[0020] FIG. 31 schematically shows a sectional view of a solar cell
string having the solar cells of the configuration of FIG. 26
connected in series. Interconnector 31 secured by means of
soldering or the like to bus bar electrode 13a at the
light-receiving face of a solar cell is fastened to silver
electrode 16 located at the back side of another adjacent solar
cell by means of soldering. In FIG. 31, the n+ layer, p+ layer and
anti-reflection film are not depicted.
[0021] Patent Document 1: Japanese Patent Laying-Open No.
2005-142282
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0022] The rapid proliferation of photovoltaic power generation
systems has necessitated reduction in the fabrication cost of solar
cells. Rendering larger and thinner the silicon substrate that is a
semiconductor substrate are effective means for reducing the
fabrication cost of solar cells. However, a larger and thinner
silicon substrate provides the disadvantage that warpage will occur
at the solar cell, leading to the possibility of a crack being
generated at the light-receiving face of the solar cell in contact
with a bus bar electrode of the solar cell, since an interconnector
formed of copper contracts more greatly than the solar cell due to
the difference in the thermal expansion coefficient between the
silicon substrate of the solar cell and the interconnector (the
thermal expansion coefficient of silicon is 3.5.times.10.sup.-6/K
whereas the thermal expansion coefficient of copper is
17.6.times.10.sup.-6/K, which is approximately 5 times larger)
during a cooling step subsequent to a heating step in which a bus
bar electrode at the light-receiving face of the solar cell and an
interconnector are fastened by soldering and the like for
connection, in the production of a solar cell string.
[0023] Patent Document 1 (Japanese Patent Laying-Open No.
2005-142282) discloses the method of providing a small
cross-sectional area section where the cross-sectional area is
locally reduced at the interconnector that connects adjacent solar
cells. A concave warpage occurs at the solar cell when the
interconnector and solar cell in a heated state by the
aforementioned heating step are cooled down to the room
temperature, as described above. At this stage, the ability to
return to its former shape (resilience) is generated at the solar
cell. This resilience applies tensile stress to the interconnector.
According to the method disclosed in Patent Document 1, the small
cross-sectional area section of the interconnector where the
strength is relatively lower as compared to other portions is
elongated when tensile stress is applied to the interconnector to
reduce the warpage at the solar cell. There is, however, a desire
for further improvement.
[0024] A possible approach to reduce the warpage at a solar cell is
to produce a solar cell string by connecting solar cells having the
electrodes at the light-receiving face based on a configuration
shown in FIGS. 32 and 33 and the electrodes at the back side based
on a configuration shown in FIG. 34, employing the interconnector
disclosed in Patent Document 1. This solar cell string is
exemplified in FIG. 35 corresponding to a schematic sectional view,
and in FIG. 36 corresponding to a schematic enlarged plan view of
the solar cell string of FIG. 35, viewed from the light-receiving
face side.
[0025] As shown in FIGS. 32 and 33, silver electrode 13 formed on
the light-receiving face that is the first main surface of p-type
silicon substrate 10 of a solar cell includes one linear bus bar
electrode 13a of a relatively large width, and a plurality of
linear finger electrodes 13b having a relatively small width,
extending from bus bar electrode 13a. Bus bar electrode 13a
includes a linear first connecting portion 51 fastened to an
interconnector for connection, and a first non-connecting portion
42 that is not connected to an interconnector. First connecting
portion 51 and first non-connecting portion 42 are arranged
alternately along the longitudinal direction of bus bar electrode
13a. Second non-connecting portion 42 is electrically connected to
adjacent first connecting portions 51 located at both sides.
[0026] The surface contour of first connecting portion 51 is
rectangular. The surface contour of an inside region 43 that is a
void, adjacent to an end face of first connecting portion 51 and a
side face of first non-connecting portion 42 is also
rectangular.
[0027] Referring to FIG. 34, aluminium electrode 14 is formed
nearly all over the second main surface of p-type silicon substrate
10. Silver electrode 16 is formed only at a portion of the second
main surface of p-type silicon substrate 10. Here, silver
electrodes 16 will be the second connecting portion to be fastened
to the interconnector for connection. Aluminium electrode 14
located between silver electrodes 16 will be a second
non-connecting portion 14a that is not connected to an
interconnector. The second main surface of p-type silicon substrate
10 that is the semiconductor substrate is located opposite to the
first main surface of p-type silicon substrate 10 that is the
semiconductor substrate.
[0028] In the solar cell string of FIG. 35 employing the
interconnector disclosed in Patent Document 1, interconnector 31
fastened and connected by soldering or the like to first connecting
portion 51 at the light-receiving face of the solar cell is
fastened and connected to silver electrode 16 at the back side of
another solar cell located adjacent by soldering or the like. In
FIG. 35, the n+ layer, p+ layer, and anti-reflection film are not
depicted.
[0029] Referring to FIGS. 35 and 36, small cross-sectional area
section 41 of interconnector 31 is located at inside region 43 and
second non-connecting portion 14a of the solar cell, and is not
fastened by soldering or the like. Therefore, when tensile stress
is applied to interconnector 31, small cross-sectional area section
41 of relatively low strength as compared to other portions can
elongate arbitrarily, allowing reduction in the warpage at the
solar cell.
[0030] However, this solar cell string had the possibility of a
crack being generated in a solar cell at the interface section
between first connecting portion 51 and inside region 43 at the
light-receiving face of the solar cell constituting the solar cell
string due to the warpage occurring at the solar cell in the
cooling step subsequent to interconnector connection. Therefore,
improvement thereof was desired.
[0031] In view of the foregoing, an object of the present invention
is to provide a solar cell, a solar cell string, and a solar cell
module that can have generation of a crack in the solar cell
reduced when warpage occurs at the solar cell in a cooling step
subsequent to interconnector connection.
Means for Solving the Problems
[0032] The present invention is directed to a solar cell including
a semiconductor substrate having a photoelectric converting
portion, a first electrode formed on a first main surface of the
semiconductor substrate, and a second electrode electrically
connected to the first electrode on the first main surface. The
first electrode includes a plurality of first connecting portions
to be connected to an interconnector, and a first non-connecting
portion not connected to an interconnector. The first
non-connecting portion is arranged between the first connecting
portions to electrically connect the first connecting portions
together. The first connecting portion and the first non-connecting
portion are coupled forming an angle larger than 90.degree. and
smaller than 180.degree..
[0033] In the solar cell of the present invention, the first
non-connecting portion may extend from an end face of the first
connecting portion.
[0034] In the solar cell of the present invention, the first
non-connecting portion may extend from a side face of the first
connecting portion.
[0035] In the solar cell of the present invention, the first
non-connecting portion may be formed of a combination of straight
portions.
[0036] In the solar cell of the present invention, the first
non-connecting portion may include an arc portion.
[0037] In the solar cell of the present invention, the
cross-sectional area of the first non-connecting portion is
preferably not more than 1/2 the cross-sectional area of the first
connecting portion.
[0038] In the solar cell of the present invention, a second
connecting portion to be connected to an interconnector, and a
second non-connecting portion not connected to an interconnector
may be formed alternately on a second main surface opposite to the
first main surface of the semiconductor substrate.
[0039] The solar cell of the present invention preferably includes
a portion where the first connecting portion and the second
connecting portion are located symmetric about the semiconductor
substrate.
[0040] Further, the present invention is directed to a solar cell
string including a plurality of solar cells set forth above
connected. With regards to solar cells adjacent to each other, the
first connecting portion of a first solar cell and the second
connecting portion of a second solar cell are electrically
connected by an interconnector in the solar cell string.
[0041] In the solar cell string of the present invention, the
interconnector may be bent between the first solar cell and the
second solar cell.
[0042] In the solar cell string of the present invention, a small
cross-sectional area section having the cross-sectional area of the
interconnector locally reduced is preferably arranged at at least
one of a site corresponding to an inside region, adjacent to a side
face of the first non-connecting portion and an end face of the
first connecting portion, and a site corresponding to the second
non-connecting portion.
[0043] In addition, the present invention is directed to a solar
cell module including the solar cell string set forth above sealed
with a sealant.
[0044] In the solar cell of the present invention, at least one of
the first connecting portions adjacent to an end of the first main
surface may be arranged apart from the end of the first main
surface.
[0045] In the solar cell of the present invention, the surface
contour of the inside region adjacent to a side face of the first
non-connecting portion and an end face of the first connecting
portion preferably takes a shape of an arc at a leading end portion
of the first connecting portion side.
[0046] In the solar cell of the present invention, the surface
contour of the inside region preferably takes the shape of a
circle, an ellipse, or a track.
[0047] In the solar cell of the present invention, a second
connecting portion to be connected to an interconnector and a
second non-connecting portion not connected to an interconnector
are preferably formed alternately on a second main surface opposite
to the first main surface of the semiconductor substrate.
[0048] In the solar cell of the present invention, the length of
the inside region in a direction of arrangement of the first
connecting portion and the first non-connecting portion may be
shorter than the length of the second non-connecting portion,
opposite to the inside region with the semiconductor substrate
therebetween, in the direction of arrangement of the second
connecting portion and the second non-connecting portion.
[0049] The solar cell of the present invention may include a
portion where the second non-connecting portion is not formed at a
location symmetric to the location where the inside region is
formed, about the semiconductor substrate.
[0050] Moreover, the present invention is directed to a solar cell
string including a plurality of solar cells set forth above
connected. With regards to solar cells adjacent to each other, the
first connecting portion of a first solar cell and the second
connecting portion of a second solar cell are electrically
connected by an interconnector.
[0051] In the solar cell string of the present invention, a small
cross-sectional area section of an interconnector having the
cross-sectional area locally reduced is preferably arranged at at
least one of a site corresponding to the inside region and a site
corresponding to the second non-connecting portion.
[0052] Furthermore, the present invention is directed to a solar
cell module including the solar cell string set forth above sealed
with a sealant.
EFFECTS OF THE INVENTION
[0053] According to the present invention, there can be provided a
solar cell, a solar cell string, and a solar cell module that can
have generation of a crack in a solar cell reduced when warpage
occurs at the solar cell in a cooling step subsequent to
interconnector connection.
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] FIG. 1 is a schematic plan view of an example of a
configuration of electrodes formed on a first main surface of a
p-type silicon substrate that is the light-receiving face of a
solar cell of the present invention.
[0055] FIG. 2 is a schematic enlarged plan view of the neighborhood
of the first non-connecting portion of FIG. 1.
[0056] FIG. 3 is a schematic plan view of an example of a
configuration of electrodes formed on a second main surface that is
the back side of the solar cell of the present invention.
[0057] FIG. 4 is a schematic sectional view of an example of a
solar cell string of the present invention, formed by connecting in
series solar cells having electrodes at the light-receiving face
based on the configuration of FIG. 1 face and electrodes at the
back side based on the configuration of FIG. 3.
[0058] FIG. 5 is a schematic enlarged plan view of the solar cell
string of FIG. 4, viewed from the light-receiving face side.
[0059] FIG. 6 is a schematic enlarged plan view of another example
of a bus bar electrode, in the neighborhood of the first
non-connecting portion, formed on the first main surface of the
solar cell of the present invention.
[0060] FIG. 7 is a schematic enlarged plan view of another example
of a bus bar electrode, in the neighborhood of the first
non-connecting portion, formed on the first main surface of the
solar cell of the present invention.
[0061] FIG. 8 is a schematic enlarged plan view of another example
of a bus bar electrode, in the neighborhood of the first
non-connecting portion, formed on the first main surface of the
solar cell of the present invention.
[0062] FIG. 9 is a schematic enlarged plan view of another example
of a bus bar electrode, in the neighborhood of the first
non-connecting portion, formed on the first main surface of the
solar cell of the present invention.
[0063] FIG. 10 is a schematic enlarged plan view of another example
of a bus bar electrode, in the neighborhood of the first
non-connecting portion, formed on the first main surface of the
solar cell of the present invention.
[0064] FIG. 11 is a schematic enlarged plan view corresponding to
an exemplified state of an interconnector having a configuration
different from that of the interconnector of FIG. 5, electrically
connected to the electrodes at the light-receiving face based on
the configuration shown in FIG. 1.
[0065] FIG. 12 is a schematic sectional view of an example of a
solar cell string formed by electrically connecting in series a
plurality of solar cells having electrodes at the light-receiving
face based on the configuration of FIG. 1 and electrodes at the
back side based on the configuration of FIG. 3, by means of the
interconnector of FIG. 11.
[0066] FIG. 13 is a schematic plan view of a light-receiving face
identified as a first main surface of an example of a solar cell of
the present invention.
[0067] FIG. 14 is a schematic plan view of the back side identified
as a second main surface of the solar cell of FIG. 13.
[0068] FIG. 15 is a schematic plan view taken along line XV-XV of
FIGS. 13 and 14.
[0069] FIG. 16 is a schematic plan view of a light-receiving face
identified as a first main surface of another example of a solar
cell of the present invention.
[0070] FIG. 17 is a schematic plan view of the back side of the
solar cell of FIG. 16, identified as a second main surface.
[0071] FIG. 18 is a schematic sectional view taken along line
XVIII-XVIII of FIGS. 16 and 17.
[0072] FIG. 19 is a schematic plan view of an example of an
interconnector employed in a solar cell string of the present
invention.
[0073] FIG. 20 is a schematic plan view of another example of an
interconnector employed in the present invention.
[0074] FIG. 21 is a schematic plan view of another example of an
interconnector employed in the present invention.
[0075] FIG. 22 is a schematic plan view of another example of an
interconnector employed in the present invention.
[0076] FIG. 23 is a schematic sectional view of an example of a
solar cell string of the present invention, formed by connecting in
series solar cells having the light-receiving face of FIG. 13 and
the back side of FIG. 14.
[0077] FIG. 24 is a schematic enlarged plan view of the solar cell
string of FIG. 23, viewed from the light-receiving face side.
[0078] FIG. 25 is a schematic plan view of another example of an
interconnector employed in the present invention.
[0079] FIG. 26 is a schematic sectional view of an example of a
conventional solar cell.
[0080] FIG. 27 is a diagram to illustrate an example of a
fabrication method of a conventional solar cell.
[0081] FIG. 28 is a diagram to illustrate an example of a
fabrication method of a conventional solar cell module.
[0082] FIG. 29 is a schematic plan view of a configuration of a
silver electrode formed on a first main surface of a p-type silicon
substrate that is the light-receiving face of the solar cell of
FIG. 26.
[0083] FIG. 30 is a schematic plan view of a configuration of an
aluminium electrode and silver electrode formed on a second main
surface of a p-type silicon substrate that is the back side of the
solar cell of FIG. 26.
[0084] FIG. 31 is a schematic sectional view of a solar cell string
having solar cells of the configuration of FIG. 26 connected in
series.
[0085] FIG. 32 is a schematic plan view of an example of a
configuration of electrodes at the light-receiving face of a solar
cell.
[0086] FIG. 33 is a schematic enlarged plan view of electrodes at
the light-receiving face of FIG. 32, in the neighborhood of a first
non-connecting portion.
[0087] FIG. 34 is a schematic plan view of an example of a
configuration of electrodes at the back side of a solar cell.
[0088] FIG. 35 is a schematic sectional view of an example of a
solar cell string formed by connecting solar cells having
electrodes at the light-receiving face based on the configuration
shown in FIGS. 32 and 33 and electrodes at the back side based on
the configuration shown in FIG. 34, by means of an interconnector
disclosed in Patent Document 1.
[0089] FIG. 36 is a schematic enlarged plan view of the
light-receiving face of the solar cell string of FIG. 35.
DESCRIPTION OF THE REFERENCE CHARACTERS
[0090] 10 p-type silicon substrate, 11 n+ layer, 12 anti-reflection
film, 13 silver electrode, 13a bus bar electrode, 13b finger
electrode, 14 aluminium electrode, 14a second non-connecting
portion, 15 p+ layer, 16 silver electrode, 17 silicon ingot, 18
silicon block, 19 damage layer, 20 dopant solution, 30 solar cell,
31 interconnector, 33 wiring material, 34 solar cell string, 35
glass sheet, 36 EVA film, 37 back film, 38 terminal box, 39 cable,
40 aluminium frame, 41 small cross-sectional area section, 42 first
non-connecting portion, 43 inside region, 51 first connecting
portion, 80 first solar cell, 81 second solar cell
BEST MODES FOR CARRYING OUT THE INVENTION
[0091] Embodiments of the present invention will be described
hereinafter. In the drawings of the present invention, the same
reference characters denote the same or corresponding elements.
[0092] FIG. 1 is a schematic plan view of an example of the
configuration of electrodes formed on a first main surface of a
p-type silicon substrate 10 that is the light-receiving face of a
solar cell of the present invention. The electrodes formed on the
first main surface include a bus bar electrode 13a of a relatively
large width, serving as a first electrode, extending horizontally
in the drawing sheet, and a plurality of linear finger electrodes
13b of a relatively small width, serving as the second electrode,
extending from bus bar electrode 13a in the vertical direction in
the drawing sheet. Although FIG. 1 shows bus bar electrode 13a and
finger electrode 13b arranged orthogonal to each other, the
positional relationship thereof can be modified appropriately.
[0093] Bus bar electrode 13a includes a first connecting portion 51
of linear form, fastened to and electrically connected to an
interconnector, and a first non-connecting portion 42 not connected
to an interconnector. First connecting portion 51 and first
non-connecting portion 42 are arranged alternately along the
longitudinal direction of bus bar electrode 13a. The electrodes at
the light-receiving face of FIG. 1 are configured such that at
least one of first connecting portions 51 adjacent to the end of
the first main surface of p-type silicon substrate 10 is disposed
apart from the end of the first main surface.
[0094] FIG. 2 is a schematic enlarged plan view in the neighborhood
of first non-connecting portion 42 of FIG. 1. As shown in FIG. 2,
first non-connecting portion 42 electrically connects adjacent
first connecting portions 51 together. On the first main surface is
also provided an inside region 43 that is a void, adjacent to an
end face of first connecting portion 51 and a side face of first
non-connecting portion 42. First non-connecting portion 42 extends
from a side face of a first connecting portion 51. First
non-connecting portion 42 and first connecting portion 51 form an
angle .alpha. of approximately 150.degree., which is larger than
90.degree. and smaller than 180.degree..
[0095] By the configuration of setting angle .alpha. between first
non-connecting portion 42 and first connecting portion 51 larger
than 90.degree. and smaller than 180.degree. in the solar cell of
the present invention, generation of a crack in the solar cell can
be reduced, at the interface section between first connecting
portion 51 and inside region 43 at the light-receiving face of the
solar cell constituting a solar cell string, caused by warpage
occurring at the solar cell during a cooling step subsequent to
interconnector connection.
[0096] Although the reason is not definite, it is considered that
the stress received at the interface section between first
connecting portion 51 and inside region 43 at the solar cell is
dispersed when warpage occurs at the solar cell during the cooling
step subsequent to interconnector connection, by coupling first
non-connecting portion 42 and first connecting portion 51 at an
angle larger than 90.degree. and smaller than 180.degree..
[0097] When it is assumed that the length of inside region 43 in
the solar cell of the present invention having the configuration
set forth above (the length in the direction of arrangement of
first connecting portion 51 and first non-connecting portion 42) is
equal to the length of inside region 43 in the electrode at the
light-receiving face based on the configuration shown in FIGS. 32
and 33 (the length in the direction of arrangement of first
connecting portion 51 and first non-connecting portion 42), the
shortest distance of the overall length of first non-connecting
portion 42 in the solar cell of the present invention is shorter
than the shortest distance of the overall length of first
non-connecting portion 42 in the electrode at the light-receiving
face based on the configuration shown in FIGS. 32 and 33.
[0098] Therefore, since the overall length of first non-connecting
portion 42 in the solar cell of the present invention is shorter
than the overall length of first non-connecting portion 42 in the
electrode at the light-receiving face based on the configuration
shown in FIGS. 32 and 33 when the length of inside region 43 is
identical, the electric resistance at first non-connecting portion
42 in the solar cell of the present invention becomes lower than
the electric resistance at first non-connecting portion 42 in the
electrode at the light-receiving face based on the configuration
shown in FIGS. 32 and 33.
[0099] Accordingly, the property of the solar cell of the present
invention having the configuration set forth above is favorable
than that of a solar cell having electrodes at the light-receiving
face based on the configuration shown in FIGS. 32 and 33.
[0100] Since first non-connecting portion 42 does not overlap an
interconnector, the region of the light-receiving face where first
non-connecting portion 42 is disposed will correspond to a
shadow-loss region. Therefore, when the width of first
non-connecting portion 42 in the solar cell of the present
invention is equal to the width of first non-connecting portion 42
in the solar cell having electrodes at the light-receiving face
based on the configuration shown in FIGS. 32 and 33, the
shadow-loss region in the solar cell of the present invention can
be reduced as compared to that of the solar cell based on the
configuration shown in FIGS. 32 and 33, by the shorter width of
first non-connecting portion 42.
[0101] The possibility of first non-connecting portion 42 being
faded in print can be reduced since the overall length of first
non-connecting portion 42 can be made shorter as compared to the
solar cell having electrodes at the light-receiving face based on
the configuration of FIGS. 32 and 33. Therefore, the electric
resistance up to first connecting portion 51 from finger electrode
13b that is connected to first non-connecting portion 42 can be
further reduced. As a result, the yield of solar cells is improved
according to the present invention since fabrication of solar cells
of low property can be suppressed.
[0102] In the configuration shown in FIG. 2, the width of first
non-connecting portion 42, first connecting portion 51, and finger
electrode 13b is, but not limited to, 0.3 mm, 2.5 mm, and 0.16 mm,
respectively. Further, although first non-connecting portion 42 is
configured by a combination of three straight portions in FIG. 2,
the configuration is not limited thereto.
[0103] FIG. 3 represents a schematic plan view of an example of a
configuration of electrodes formed on the second main surface that
is the back side of the solar cell of the present invention.
[0104] An aluminium electrode 14 is formed nearly all over the
second main surface of the solar cell of the present invention. On
the region of the second main surface excluding the region where
aluminium electrode 14 is formed, a straight silver electrode 16,
identified as the second connecting portion that is to be connected
to an interconnector, is formed extending in the horizontal
direction of the drawing sheet. The region of aluminium electrode
14 located between adjacent silver electrodes 16 is a second
non-connecting portion 14a that is not connected to an
interconnector. Silver electrode 16 that is the second connecting
portion and second non-connecting portion 14a are arranged
alternately.
[0105] FIG. 4 is a schematic sectional view of an example of a
solar cell string of the present invention, formed by connecting in
series solar cells having electrodes at the light-receiving face
based on the configuration shown in FIG. 1 and electrodes at the
back side based on the configuration shown in FIG. 3. FIG. 5 is a
schematic enlarged plan view of the solar cell string of FIG. 4,
viewed from the light-receiving face side. For the sake of
convenience, the n+ layer, p+ layer and anti-reflection film formed
at p-type silicon substrate 10 are not depicted in FIG. 4.
[0106] In adjacent solar cells in the solar cell string of the
present invention, first connecting portion 51 of a first solar
cell 80 and silver electrode 16 that is the second connecting
portion of a second solar cell 81 are fastened to and electrically
connected to interconnector 31 by soldering or the like. In the
present invention, the shape and material of the interconnector are
not particularly limited, as long as the interconnector is a member
having conductivity.
[0107] In the solar cell of the present invention, first connecting
portion 51 and silver electrode 16 that is the second connecting
portion are located symmetric about p-type silicon substrate 10
that is the semiconductor substrate.
[0108] In a solar cell string of the present invention having the
above-described configuration, interconnector 31 is not connected
at the region of the solar cell corresponding to inside region 43
at the light-receiving face and second non-connecting portion 14a
at the back side.
[0109] Therefore, during the cooling step subsequent to connection
of interconnector 31 in the process of fabricating a solar cell
string of the present invention, the inner stress generated at the
solar cell due to the difference in the thermal expansion
coefficient between interconnector 31 and the solar cell can be
alleviated by the region of the interconnector that is not fastened
to inside region 43 and second non-connecting portion 14a. Thus,
the warpage in the solar cell constituting the solar cell string
can be reduced.
[0110] Since first connecting portion 51 fastened to interconnector
31 and silver electrode 16 that is the second connecting portion
are arranged symmetric about p-type silicon substrate 10 that is
the semiconductor substrate, the inner stress generated at the
solar cell caused by the difference in the thermal expansion
coefficient between the solar cell and interconnector 31 can be set
substantially equal between the light-receiving face and the back
side of the solar cell. Therefore, the warpage at the solar cell
constituting a solar cell string can be further reduced.
[0111] Since the solar cell string of the present invention is
formed by a solar cell having electrodes at the light-receiving
face based on the configuration of FIG. 1 and electrodes at the
back side based on the configuration of FIG. 3, the generation of a
crack in a solar cell can be reduced at the interface section
between first connecting portion 51 and inside region 43 located at
the light-receiving face of the solar cell.
[0112] FIG. 6 is a schematic enlarged plan view of another example
of bus bar electrode 13a, in the neighborhood of first
non-connecting portion 42, formed on the first main surface of the
solar cell of the present invention. The configuration of FIG. 6 is
characterized in that the angle .alpha. between first
non-connecting portion 42 and first connecting portion 51 is
approximately 135.degree., which is smaller than that
(approximately 150.degree.) of FIG. 2, and that first
non-connecting portion 42 extends from a side face of first
connecting portion 51. The configuration of FIG. 6 is prone to
further reduce the warpage in the solar cell constituting the solar
cell string since first non-connecting portion 42 and
interconnector 31 are not fastened, and the connecting region
between bus bar electrode 13a of the solar cell and interconnector
31 can be reduced, even in the case where the width of first
connecting portion 51 and the width of interconnector 31 are
identical.
[0113] FIG. 7 is a schematic enlarged plan view of another example
of a bus bar electrode 13a, in the neighborhood of first
non-connecting portion 42, formed on the first main surface of the
solar cell of the present invention. The configuration of FIG. 7 is
characterized in that the angle .alpha. between first
non-connecting portion 42 and first connecting portion 51 is
approximately 150.degree., and that first non-connecting portion 42
extends from an end face of first connecting portion 51. In the
configuration of FIG. 7, there is a tendency of first
non-connecting portion 42 not fastened to interconnector 31 when
the width of interconnector 31 is set smaller than the width of
first connecting portion 51. Since the connecting region between
bus bar electrode 13a of the solar cell and interconnector 31 can
be reduced, there is a tendency to further reduce warpage in the
solar cells constituting the solar cell string.
[0114] FIG. 8 is a schematic enlarged plan view of another example
of a bus bar electrode 13a, in the neighborhood of first
non-connecting portion 42, formed on the first main surface of the
solar cell of the present invention. The configuration of FIG. 8 is
characterized in that first non-connecting portion 42 is formed
including an arc portion, extending from a side face of first
connecting portion 51. The configuration of FIG. 8 is prone to
further reduce warpage in the solar cell constituting the solar
cell string since first non-connecting portion 42 and
interconnector 31 are not fastened and the connecting region
between bus bar electrode 13a of the solar cell and interconnector
31 can be reduced, even in the case where the width of first
connecting portion 51 and the width of interconnector 31 are set
identical. It is apparent from the configuration of FIG. 8 that
first non-connecting portion 42 and first connecting portion 51
form an angle .alpha. that is larger than 90.degree. and smaller
than 180.degree..
[0115] FIG. 9 is a schematic enlarged plan view of another example
of a bus bar electrode 13a, in the neighborhood of first
non-connecting portion 42, formed on the first main surface of the
solar cell of the present invention. The configuration of FIG. 9 is
characterized in that first non-connecting portion 42 is formed
including an arc portion, extending from an end face of first
connecting portion 51. The configuration of FIG. 9 is prone to
further reduce warpage in the solar cell constituting the solar
cell string since first non-connecting portion 42 and
interconnector 31 are not fastened and the connecting region
between bus bar electrode 13a of the solar cell and interconnector
31 can be reduced in the case where the width of first connecting
portion 51 is set larger than the width of interconnector 31. It is
apparent from the configuration of FIG. 9 that first non-connecting
portion 42 and first connecting portion 51 form an angle .alpha.
that is larger than 90.degree. and smaller than 180.degree..
[0116] FIG. 10 is a schematic enlarged plan view of another example
of a bus bar electrode 13a, in the neighborhood of first
non-connecting portion 42, formed on the first main surface of the
solar cell of the present invention. The configuration of FIG. 10
is characterized in that the width of first non-connecting portion
42 is 0.6 mm, which is two times that (0.3 mm) of the configuration
of FIG. 2. The configuration of FIG. 10 is prone to reduce the
electrical resistance at first non-connecting portion 42 due to the
larger width of first non-connecting portion 42.
[0117] It is preferable to set the cross-sectional area of first
non-connecting portion 42 (the area of the cross section in the
direction orthogonal to the longitudinal direction of first
non-connecting portion 42) to be not more than 1/2 the
cross-sectional area of first connecting portion 51 (the area of
the cross section in the direction orthogonal to the longitudinal
direction of first connecting portion 51). This is because, if the
cross-sectional area of first non-connecting portion 42 (the area
of the cross section in the direction orthogonal to the
longitudinal direction of first non-connecting portion 42) is set
larger than 1/2 the cross-sectional area of first connecting
portion 51 (the area of the cross section in the direction
orthogonal to the longitudinal direction of first connecting
portion 51), the amount of electrode material used cannot be
reduced as compared to the case where bus bar electrode 13a is
formed of first connecting portion 51 alone, absent of first
non-connecting portion 42.
[0118] In the configuration of FIG. 10, the angle .alpha. between
first non-connecting portion 42 and first connecting portion 51 is
approximately 150.degree..
[0119] FIG. 11 is a schematic enlarged plan view corresponding to
an exemplified state of an interconnector having a configuration
different from that of the interconnector of FIG. 5, electrically
connected to the electrodes at the light-receiving face based on
the configuration shown in FIG. 1. Interconnector 31 of FIG. 11 has
small notches formed, constituting a small cross-sectional area
section 41. In FIG. 11, small cross-sectional area section 41 of
interconnector 31 is located at a site corresponding to inside
region 43. In the present invention, a "small cross-sectional area
section" refers to the section of the interconnector where the area
of the cross section orthogonal to the longitudinal direction is
locally reduced.
[0120] FIG. 12 is a schematic sectional view of an example of a
solar cell string formed by electrically connecting in series a
plurality of solar cells having the electrodes at the
light-receiving face based on the configuration of FIG. 1 and the
electrodes at back side based on the configuration shown in FIG. 3,
using interconnector 31 of FIG. 11.
[0121] The solar cell string of FIG. 12 has first connecting
portion 51 of first solar cell 80 and silver electrode 16 that is
the second connecting portion of second solar cell 81, adjacent to
each other, electrically connected by interconnector 31.
Interconnector 31 is bent between first solar cell 80 and second
solar cell 81. Small cross-sectional area section 41 of
interconnector 31 is located at all the sites corresponding to each
inside region 43 and each second non-connecting portion 14a.
[0122] By connecting interconnector 31 such that small
cross-sectional area section 41 of interconnector 31 is located at
at least one of the sites corresponding to inside region 43 and
second non-connecting portion 14a, preferably located at all the
sites, the advantage of further alleviating the stress by the
elongation of small cross-sectional area section 41 that is
relatively low in strength as compared to other portions of
interconnector 31 is provided, in addition to the aforementioned
reduction in stress. Specifically, in the case where small
cross-sectional area section 41 of interconnector 31 is located
corresponding to both inside region 43 and second non-connecting
portion 14a, arbitrary deformation is allowed since small
cross-sectional area section 41 is not fastened and takes a free
state. The stress alleviation effect by the elongation can be
exhibited sufficiently. In this case, generation of a crack in the
solar cell can be reduced significantly at the interface section
between first connecting portion 51 and inside region 43 at the
light-receiving face of the solar cell caused by the warpage
occurring at the solar cell during a cooling step subsequent to
interconnector connection.
[0123] FIG. 13 is a schematic plan view of a light-receiving face
that is the first main surface according to an example of a solar
cell of the present invention. The solar cell employs a p-type
single crystal silicon for the material of p-type silicon substrate
10, including a linear bus bar electrode 13a of a relatively large
width, extending vertically in the drawing sheet, and a plurality
of linear finger electrodes 13b of small width, extending in the
horizontal direction in the drawing sheet from bus bar electrode
13a, at the first main surface of p-type silicon substrate 10 that
is the light-receiving face of the solar cell.
[0124] Bus bar electrode 13a includes first connecting portion 51
fastened to and electrically connected to an interconnector, and a
first non-connecting portion 42 not connected to an interconnector.
First connecting portions 51 and first non-connecting portion 42
are arranged alternately along the longitudinal direction of bus
bar electrode 13a. The electrodes at the light-receiving face of
FIG. 13 are configured such that at least one of first connecting
portions 51 adjacent to an end of the first main surface of p-type
silicon substrate 10 is disposed apart from the end of the first
main surface.
[0125] First non-connecting portion 42 extends from a side face of
first connecting portion 51. First non-connecting portion 42 and
first connecting portion 51 form an angle .alpha. larger than
90.degree. and smaller than 180.degree.. On the first main surface
is also provided an inside region 43 that is a void, adjacent to an
end face of first connecting portion 51 and a side face of first
non-connecting portion 42.
[0126] FIG. 14 is a schematic plan view of the back side of the
solar cell of FIG. 13, corresponding to the second main face. At
the second main face of p-type silicon substrate 10 identified as
the back side of the solar cell of the present invention, silver
electrode 16 that is the second connecting portion for connection
to an interconnector, and second non-connecting portion 14a not
connected to an interconnector, are formed alternately. Second
non-connecting portion 14a is formed of aluminium electrode 14
between adjacent silver electrodes 16 in the longitudinal direction
of silver electrode 16 that is the second connecting portion.
[0127] The solar cell is characterized in that, as shown in FIG.
13, the surface contour of inside region 43 corresponds to a track
shape with an arc shape at the leading end located at the side of
first connecting portion 51 (semi-circles at both ends, joined by
two straight segments).
[0128] This is based on the findings made by the inventors as a
result of diligent research. Namely, generation of a crack in a
solar cell caused by the warpage occurring at the solar cell during
a cooling step subsequent to interconnector connection in the
fabrication of a solar cell string can be reduced at the interface
section between first connecting portion 51 and inside region 43 at
the light-receiving face of the solar cell by forming the interface
section between first connecting portion 51 and inside region 43 in
an arc shape. Although the reason thereof is not definite, it is
considered that the stress received at the interface section
between first connecting portion 51 and inside region 43 of the
solar cell is dispersed when warpage occurs at the solar cell
during the cooling step subsequent to interconnector connection by
forming the interface section between first connecting portion 51
and inside region 43 in an arc shape.
[0129] FIG. 15 is a schematic sectional view taken along line XV-XV
of FIGS. 13 and 14. As shown in FIGS. 13 to 15, a length L1 of
inside region 43 in the direction of arrangement of first
connecting portion 51 and first non-connecting portion 42 (the
vertical direction in the drawing sheet of FIG. 1) is preferably
shorter than a length L2 of a companion second non-connecting
portion 14a in the direction of arrangement of the second
connecting portion and second non-connecting portion 14a (vertical
direction in the drawing sheet of FIG. 2).
[0130] This is based on the findings made by the inventors as a
result of diligent research. Namely, generation of a crack at the
interface between first connecting portion 51 and inside region 43
at the light-receiving face of the solar cell constituting the
solar cell string can be further reduced by setting length L1 of
inside region 43 shorter than length L2 of second non-connecting
portion 14a located opposite to inside region 43 with p-type
silicon substrate 10 therebetween. It is considered that the
generation of a crack in the solar cell can be further reduced at
the interface section between first connecting portion 51 and
inside region 43 at the light-receiving face of the solar cell when
warpage occurs at the solar cell during a cooling step subsequent
to interconnector connection since aluminium constituting second
non-connecting portion 14a that is longer than inside region 43
serves to provide a reinforcing effect.
[0131] The advantage set forth above can be obtained as long as at
least one set of inside region 43 and second non-connecting portion
14a is located facing each other with p-type silicon substrate 10
therebetween, and at least one of the sets of inside region 43 and
second non-connecting portion 14a facing each other is provided
such that a length L1 of inside region 43 is shorter than a length
L2 of second non-connecting portion 14a.
[0132] The solar cell of the present invention may include a
portion where second non-connecting portion 14a is not formed at
the location symmetric to the location where inside region 43 is
formed about p-type silicon substrate 10, as shown in the right end
of FIG. 15.
[0133] FIG. 16 is a schematic plan view of the light-receiving face
that is the first main surface of another example of a solar cell
of the present invention. FIG. 17 is a schematic plan view of the
back side that is the second main surface of the solar cell of FIG.
16. FIG. 18 is schematic sectional view taken along line
XVIII-XVIII of FIGS. 16 and 17. The solar cell is characterized in
that p-type polycrystalline silicon is employed for the material of
p-type silicon substrate 10. The remaining elements are similar to
those set forth above.
[0134] FIG. 19 is a schematic plan view of an example of an
interconnector employed in the solar cell string of the present
invention. Interconnector 31 includes a plurality of small
cross-sectional area sections 41 whose area of a cross section
perpendicular to the longitudinal direction of interconnector 31 is
locally reduced.
[0135] Each of FIGS. 20-22 is a schematic plan view of other
examples of an interconnector employed in the present invention.
Each interconnector 31 has a small cross-sectional area section 41
with the cross-sectional area of interconnector 31 reduced
locally.
[0136] FIG. 23 is a schematic sectional view of an example of a
solar cell string of the present invention, formed by connecting in
series a solar cell having the light-receiving face shown in FIG.
13 and the back side shown in FIG. 14. FIG. 24 is a schematic
enlarged plan view of the solar cell string of FIG. 23, viewed from
the light-receiving face side.
[0137] Interconnector 31 formed of one conductive member has one
end fastened and connected to first connecting portion 51 of a
first solar cell 80 and the other end fastened and connected to
silver electrode 16 that is the second connecting portion of a
second solar cell 81. Interconnector 31 has small cross-sectional
area section 41 arranged at inside region 43 at the light-receiving
face of first solar cell 80 and at second non-connecting portion
14a at the back side of second solar cell 81. Inside region 43 and
second non-connecting portion 14a of the solar cell are not
fastened and connected to interconnector 31. Interconnector 31 is
bent between first solar cell 80 and second solar cell 81. In FIG.
23, the anti-reflection film is not depicted.
[0138] Since the surface contour of inside region 43 of the solar
cell takes an arc shape at the leading ends located at the side of
first connecting portions 51 in the solar cell string of the
present invention, generation of a crack in a solar cell at an
interface section between first connecting portion 51 and inside
region 43 at the light-receiving face of the solar cell can be
reduced when warpage occurs at the solar cell during a cooling step
subsequent to interconnector connection, as compared to a solar
cell having the surface contour of inside region 43 as shown in
FIGS. 32 and 33, absent of an arc shape for the leading end located
at the side of first connecting portion 51.
[0139] Since interconnector 31 is not connected to first
non-connecting portion 42, inside region 43 and second
non-connecting portion 14a of the solar cell corresponding to the
configuration set forth above in the solar cell string of the
present invention, the length of connection of interconnector 31
with first connecting portion 51 and silver electrode 16 that is
the second connecting portion of the solar cell can be shortened.
In the case where the connecting length of interconnector 31 with
respect to first connecting portion 51 and silver electrode 16 that
is the second connecting portion of the solar cell is shortened,
the stress generated by the difference in the thermal expansion
coefficient between interconnector 31 and p-type silicon substrate
10 constituting a solar cell can be reduced. Therefore, generation
of a crack in a solar cell at an interface section between first
connecting portion 51 and inside region 43 at the light-receiving
face of the solar cell caused by the warpage occurring at the solar
cell during a cooling step subsequent to interconnector connection
can be further reduced.
[0140] Furthermore, by connecting interconnector 31 such that small
cross-sectional area section 41 of interconnector 31 is located at
at least one site corresponding to inside region 43 and second
non-connecting portion 14a, preferably at all the sites, the
advantage of further alleviating the stress by the elongation of
small cross-sectional area section 41 where the strength is
relatively low as compared to other portions of interconnector 31
can be provided, in addition to the aforementioned advantage of
reducing the stress. Specifically, in the case where small
cross-sectional area section 41 of interconnector 31 is located
corresponding to both inside region 43 and second non-connecting
portion 14a, arbitrary deformation is allowed since small
cross-sectional area section 41 is not fastened and takes a free
state. The stress alleviation effect by the elongation can be
exhibited sufficiently. In this case, generation of a crack in the
solar cell caused by the warpage occurring at the solar cell during
a cooling step subsequent to interconnector connection can be
reduced significantly at the interface section between first
connecting portion 51 and inside region 43 at the light-receiving
face of the solar cell.
[0141] Although a solar cell string is formed using an
interconnector of FIG. 19 in the above embodiment, a solar cell
string may be formed using an interconnector 31 shown in the
schematic plan view of FIG. 25, having small cross-sectional area
sections 41 formed equally spaced. Since formation of small
cross-sectional area section 41 is facilitated in the case where a
solar cell string is produced employing such an interconnector
having small cross-sectional area section 41 adjacent to each other
spaced equally apart, the fabrication cost of the solar cell string
can be reduced, allowing improvement in the productivity of the
solar cell string.
[0142] By sealing the above-described solar cell string of the
present invention with a sealant such as an EVA according to
well-known conventional methods, a solar cell module of the present
invention can be produced.
[0143] Elements other than those described above are similar to,
but not restricted to, those set forth in the section of the
Background Art. For example, in the present invention, a
semiconductor substrate other than a single crystal or polycrystal
p-type silicon substrate may be used. Further, the p-type and n
type conductivity can be exchanged in the description provided in
the section of the Background Art. Further, the first connecting
portion, first non-connecting portion, and second connecting
portion do not necessarily have to be silver electrodes. Moreover,
the second non-connecting portion does not necessarily have to be
an aluminium electrode, and the inside region does not necessarily
have to be a void in the present invention.
[0144] The above embodiment was described in which the surface
contour of inside region 43 takes a track shape. From the
standpoint of further reducing generation of a crack in the solar
cell at an interface section between first connecting portion 51
and inside region 43 at the light-receiving face of the solar cell
constituting a solar cell string, the surface contour of inside
region 43 preferably takes a circle, an ellipse, or a track shape
corresponding to an arc at the leading ends located at the side in
contact with first connecting portions 51.
[0145] It should be understood that the embodiments disclosed
hereinafter are illustrative and nonrestrictive in every respect.
The scope of the present invention is defined by the terms of the
claims, rather than the description above, and is intended to
include any modification within the scope and meaning equivalent to
the scope of the claims.
INDUSTRIAL APPLICABILITY
[0146] According to the present invention, there can be provided a
solar cell, a solar cell string, and a solar cell module that can
have the generation of a crack in a solar cell reduced when warpage
occurs at the solar cell during a cooling step subsequent to
interconnector connection.
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